Embodiments of the inventive subject matter generally relate to the field of computers, and, more particularly, to data backups in a redirect on write file system.
File systems employ different methods to ensure the consistency therein in the event of a system crash. One approach is for the file system to write modified data to new locations on disk in a bottom-up order every few seconds. These views of the data stored therein are called consistency snapshots. After a system crash, the file system starts with the top of the last consistency snapshot of the file system which is guaranteed to be consistent.
While the consistency snapshot is being written, new changes to the file system could be attempted by a user. It would be easy to block these changes until the consistency snapshot is committed to storage on a non-volatile machine-readable medium (e.g., hard disk). However, this approach is not acceptable because such an approach would lead to consistency snapshots not being transparent to the user. In particular, this approach can cause the entire file system to freeze every few seconds, while the consistency snapshot is being committed to storage.